This invention relates to an apparatus for exchanging lead and trail edges of sheets, and more particularly, to an improved full productivity, process speed sheet inverter apparatus that feeds a sheet into the inverter while simultaneously feeding a sheet out of the inverter at process speed.
Although a sheet inverter is referred to in the copier/printer art as an "inverter", its function is not necessarily to immediately turn the sheet over (i.e., exchange one face for the other). Its function is to effectively reverse the sheet orientation in its direction of motion. That is, to reverse the lead and trail edge orientation of the sheet. In typical inverters, the sheet is driven or fed by feed rollers or other suitable sheet driving mechanisms into a sheet reversing chute. By then reversing the motion of the sheet within the chute and feeding it back out from the chute, the desired reversal of the leading and trailing edges of the sheet in the sheet path is accomplished. Depending on the location and orientation of the inverter in a particular sheet path, this may, or may not, also accomplish the inversion (turning over) of the sheet. In some applications, for example, where the "inverter" is located at the corner of a 90.degree. to 180.degree. inherent bend in the copy sheet path, the inverter may be used to actually prevent inverting of a sheet at that point, i.e., to maintain the same side of the sheet face-up before and after this bend in the sheet path. On the other hand, if the entering and departing path of the sheet, to and from the inverter, is in substantially the same plane, the sheet will be inverted by the inverter. Thus, inverters have numerous applications in the handling of either original documents or copy sheets to either maintain or change the sheet orientation.
In the field of reprographic machines, it is often necessary to feed a copy sheet leaving the processor of the machine along one of two alternate paths, particularly when the machine can selectively produce simplex (one-sided) and duplex (two-sided) sheets. Simplex sheets may be fed directly to an output tray, whereas the duplex sheets may pass to a sheet feeder which automatically reverses the direction of movement of a simplex sheet and feeds it back into the processor, but inverted, so that the appropriate data can be applied to the second side of the sheet. Known tri-roll inverters (U.S. Pat. Nos. 4,359,217; 4,346,880; and 4,673,176) for effecting this includes three rollers in frictional or geared contact with each other, to provide two spaced-apart nips, one being an input nip to an associated downstream sheet pocket, and the other being an output nip for extracting each sheet from the pocket. U.S. Pat. No. 3,416,791 shows a document inverting apparatus that includes a solenoid actuated rotating friction roller which projects into a chute and contacts rollers movable into the chute to hold the document in engagement with the friction roller. Other inverters of general interest are included in U.S. Pat. Nos. 4,928,127; 5,033,731; and European Patent Application Publication No. 0 402 836 A2.
A reversing roll nip is sometimes used to drive a sheet out of a tri-roll inverter because it provides positive sheet control at all times and is an active device, e.g., U.S. Pat. No. 5,317,377. The rolls are reversed by means of clutches or reversing motors. The productivity of any inverter design depends on the amount of sheet overlap that can occur inside the inverter. If sheet 2 can be inverting while sheet 1 is inverting, then the inverter is more productive than a single sheet only inverter. In a reversing roll design, the amount of overlap is determined by the distance between the input rolls, gating requirements, reversing roll and inverter roll speeds, and roll acceleration and deceleration times. The reversing roll distance from the input nip is determined by the shortest sheet process length the inverter is intended to handle. Typically, this is B5 paper length. For 11.times.17 inch papers, the overlap length remains the same and skipped pitches may be required to provide extra time for the longer sheets. The requirement is that the trail edge of sheet 1 has left the reversing roll nip before the lead edge of sheet 2 reaches the reversing roll nip. In order to obtain high productivity for all sheet lengths, the reversing roll nip may be placed on a slide to accommodate different paper lengths. The slide requires a separate motor, pulleys, switches or position sensors, and tensioning cables. Input of paper size is needed to move the slide the correct distance. The slide mechanism is expensive, cumbersome, and complicated. In addition, when there is a short paper path between the fuser and the inverter, the sheet must enter the inverter at process speed.
The present invention aims at providing an inverter designed to accomplish full productivity in low, medium or high volume copier/printers by moving sheets into and/or out of the inverter at process speed i.e., the speed at which the sheets are being processed or imaged and transported by the copier/printers.